Arylpyrrole oligomers as tunable anion receptors

A novel type of arylpyrrole oligomer possessing an appropriate electropositive cavity has been designed, prepared and analysed for use as readily accessible receptors for negatively charged guests. Affinities of the receptors for various anions were determined by UV/Vis titration experiments and in depth insights into the host-guest interactions were gained by performing (1)H NMR titration experiments and X-ray crystallographic structure analyses. Experimentally determined association constants were correlated with the calculated maximum electrostatic potentials of the electropositive cavities of the receptors, allowing estimation of the strengths of host-guest associations in similar compounds. The joint contribution of aryl C-H and pyrrole N-H hydrogens was shown to be key to a strong guest association, resulting in the arylpyrrole oligomers being efficient anion receptors.